Safety device for a grinding spindle

ABSTRACT

The specification discloses a safety device for a grinding machine wheel in which the receiving head, or hub, on which the wheel is mounted is clamped to a spindle shaft by a threaded clamp element and has a guiding surface on the side facing away from the frame of the machine. The frame also has a guiding surface facing the guiding surface on the receiving head and cooperating therewith to support the receiving head radially while confining the receiving head axially in the event the threaded clamp element becomes loose on the shaft.

United States Patent Koppenwallner 1 Apr. 24, 1973 SAFETY DEVICE FOR AGRINDING [56] References Cited SPINDLE UNITED STATES PATENTS [75Inventor: Georg Koppenwallner, Weil der Stadt Germany 2,981,300 4/1961Peterson et a] ..51/168 X 3,247,621 4/1966 Aller ..51/168 X [73]Assignee: Fortuna-Werke Maschinenfabrik AG, St tt -B d C m G PrimaryExaminer-James L. Jones, Jr. many Att0rney-Walter Becker [22] Filed:Sept. 1, 1971 ABSTRACT Appl. No.: 176,992

Foreign Application Priority Data 7 Claims, 1 Drawing Figure Patented Aril 24, 1973 SAFETY DEVICE FDR A GRHNG SPHNDLE The present inventionrelates to a safety device for a grinding spindle which comprises aspindle shaft with a receiving head for the grinding tool, the headbeing arranged in overhung position. The head is by means of a threadedelement arranged coaxially with regard to the spindle axis firmlyconnected to that end of the spindle shaft which is adjacent the tool,the connection being effected by means of a device adapted to be rotatedin a direction counter to the working direction of rotation of thespindle shaft.

With spindles of this type, customarily the head for receiving thegrinding tool comprises a sleeve body connected to the spindle shaft bymeans of a conical seat and equipped with a fixed and a loose flangebetween which a grinding disc or a grinding wheel is centered andclamped fast by axially movable threadin g means. The sleeve body of thereceiving head is by a threaded element generally designed as pressingnut pressed against the cone of the spindle shaft and is therebyfrictionally connected in the direction of rotation but is notpositively connected to the spindle shaft.

It is a well known fact that with grinding spindles and, morespecifically, with grinding spindles journalled in sliding bearings aswell as spindles journalled in antifriction bearings, the possibility ofseizing and jamming of the spindle bearings is practically not excluded.When the spindle at more or less high speed is stopped at acorrespondingly strong angular retardation in view of seizing or jammingbearings, there exists the possibility that the friction between thereceiving head and the spindle shaft will not be able to cope with thecentrifugal moment of the rotating grinding disc so that the receivinghead will carry out a relative movement with regard to the spindle shaftand, more specifically, in such a direction that the threaded element orthe pressing nut will become loose. Such slipping of the receiving headwith the grinding disc in case of jamming is even desired inasmuch aswith a sudden braking of the grinding disc the danger exists that thedisc will break resulting in the inherent dangers and unavoidabledamages to the machine. These problems weigh particularly heavy inconnection with high output and high speed grinding machines. Theslipping receiving head exerts a torque upon the screw element inloosening direction against which torque the screw element can generallynot be effectively secured. The great centrifugal mass of the grindingdisc connected to the receiving head will in such an instance with thecustomary spindle designs lose its centering and may bring aboutconsiderable damage to the machine in which connection an increaseddanger exists that the grinding disc will break.

It is, therefore, an object of the present invention to provide a safetydevice in connection with grinding spindle systems of the abovementioned type, which will bring about that the braking moment actingupon the grinding disc and desired per se when the receiving head slipswill be retained if a bearing is jammed without losing the centering ofthe receiving head and the grinding disc.

This object and other objects and advantages of the invention willappear more clearly from the following specification in connection withthe accompanying drawing diagrammatically illustrating a verticalsection through the spindle axis of a grinding wheel head withprotective hood of a round grinding machine.

The safety device according to the present invention is characterizedprimarily in that within the region of the outermost end face of thereceiving head there is provided a first guiding surface which iscoaxial with the spindle axis and is non-rotatably connected to thereceiving head, and there is furthermore provided a second guidingsurface which is in fixed relationship with the frame and which, withthe receiving head firmly tightened, is associated with the firstguiding surface with play, the second guiding surface being adapted tosupport the first guiding surface at least in radial direction when thereceiving head is detached from the spindle shaft.

Referring now to the drawing in detail, the grinding wheel headgenerally designated A is mounted on a machine bed B and in receivingmeans 31 carries a grinding spindle generally designated C. The grindingspindle customarily comprises a spindle sleeve 2 with a spindle shaft lwhich is journalled therein and the lefthand end of which is adapted inany convenient or customary manner to be coupled to a drive, whereas theright-hand end of the spindle shaft 1 on a cone 17 carries a receivinghead 11 with a fixed flange 5 and a loose flange 6. A sleeve body 16 ofthe receiving head 11 is mounted on the cone l7 and by means of a screwelement 10 designed as pressing nut is non-rotatably connected to thespindle shaft merely by static friction, which means frictionally, thescrew element 10 being mounted on a threaded extension lla of spindleshaft ll.

Between the two flanges 5 and 6 of the receiving head ll and, morespecifically, centered on a shoulder of the fixed flange 5 there isclamped in axial direction by clamping screws 7 a grinding disc 4 whichis provided within a protective hood M fixedly connected to the machine.The protective hood 114 comprises substantially two parts Ma and Nbwhich in axial direction are arranged adjacent to each other. Theseparts and Mb are connected to the machine bed by triangular supportingflanges 118a and 18b. Part 14b of the protective hood 14 with thesupporting flange 18b may selectively for exchanging the grinding discor the grinding head be detached from the machine bed and may bedisplaced on the latter toward the outside.

If the bearing of the spindle shaft 1 seizes or gets jammed, thereceiving head 11 with grinding disc 4 will in general slip on the cone17 of the grinding spindle while overcoming the static friction. In suchan instance the tightened screw element 10 will be carried along in itsloosening direction and consequently will unscrew itself from thethreaded extension 1a of the spindle shaft.

it is for this disorder that the safety device according to the presentinvention is provided with a guiding surface 13 in fixed relationship tothe machine and with a guiding surface 12 arranged on the receiving head11. The two guiding surfaces form conical surfaces which, are congruentto each other and which taper at the free end of the spindle shaft B.These conical surfaces are in normal condition of operation with thereceiving head Ill in tightened condition arranged with mutual play asshown in the drawing. These conical guiding surfaces are in the specificexample shown followed by cylindrical guiding surfaces 12a and li3a. Thefixed guiding surfaces 13 and 130 are provided on an annular centeringmember 8 which by means of screws 9 is connected to the protective hoodpart 14b. All of the above mentioned guiding surfaces are coaxial withregard to the spindle shaft 1. When a bearing should jam, and subsequentto a slipping through of the receiving head, the guiding surface 12 ofthe receiving head will in response to a displacement toward the spindleend engage the fixed guiding surface 13 so that the receiving head 11will be supported in radial and axial direction and will remainsufficiently centered. In this way the danger will no longer exist thatthe grinding surfaces will impact upon'the protective hood with aresulting damage to the machine and, above all, the increased dangerthat the disc will break will thus be eliminated. Simultaneously, thecentrifugal mass of the grinding disc with receiving head will, in viewof the relatively high friction between the conical guiding surfaces, beslowly braked which means in a careful manner.

When the receiving head moves off the cone 17 of the spindle shaft whilethe play between the guiding surfaces 12 and 13 is overcome, the innerend edge of the conical bore of the sleeve body 16 of the receiving head11 is unilaterally located on the stationary cone l7 and may eventuallydamage the fitting surface of this cone. In order to prevent such asituation, that end face of the receiving head which faces toward thegrinding wheel head has connected thereto an annular supporting memberwhich may be pressed, for instance, into a corresponding recess wherebythe end edge of the conical bore of the receiving head will be covered.The supporting member 15 is made of a softer material than the conicalseat surface of the spindle shaft, for instance of aluminum, so that theabove referred to danger of damage will be excluded. In the particularexample shown, the supporting member 15 is at the same time designed asslinger ring associated with the spindle shaft bearing 19, the slingerring being adapted to prevent the entry of grinding coolant into the oilchamber of the spindle bearing.

As will be evident from the above, with a safety device according to theinvention, the receiving head 11 with grinding disc will be able, incase of a jamming of a bearing, to detach itself without difficultiesfrom the spindle shaft while the screw member is being turned loose. Inthis way the disc will be saved high braking forces while simultaneouslya sufficient centering and support of the receiving head will beretained by the guiding surfaces which will now engage each other.Moreover, the centrifugal force will now, in view of the occurringfriction between the guiding surfaces, be braked in a soft manner sothat the centrifugal mass will be stopped without the danger of breakageor damage to the'spindle or the machine.

It is, of course, to be understood that the present invention is, by nomeans, limited to the particular showing in the drawing but alsocomprises any modifications within the scope of the appended claims.

What is claimed is:

l. A safety device for a grinding machine having a frame and a spindleshaft therein and bearing means in the frame supporting the shaft withone end of the shaft projecting from the frame for receiving a grindingwheel, a receiving head seated on said projecting end of the shaft andhaving a grinding wheel mounted thereon a threaded clamp e ementthreadedly engaging the end of the shaft and clamping said receivinghead thereon and having threads of a hand such that working loads onsaid grinding wheel while it is being driven by said shaft tend totighten the threaded element on the shaft, first guiding surface meanson said receiving head coaxial with said shaft and facing away from saidframe, and second guiding surface means rigid with said frame and alsocoaxial with said shaft, said second surface facing said first surfaceand normally being spaced therefrom I but cooperating therewith toprovide radial support for said receiving head upon loosening of saidthreaded element on said shaft.

2. A safety device according to claim 1 in which said a wall portionfacing that side of said grinding wheel which faces away from saidframe, a centering member mounted in said 'wall portion so as to beintersected by the extension of the axis ofsaid shaft, and said secondsurface being formed on said centering member.

5. A safety device according to claim 1 in which the projecting end ofsaid shaft has a conical seat, said receiving head having a conical boreengaging said conical seat, and a protective element of a materialsofter than that of said shaft fixed to said receiving head on the sidethereof facing said frame to engage said seat when said threaded elementloosens to prevent said receiving head from damaging said seat. I

6. A safety device according to claim 5 in which said protective elementis in the form of a ring and has a central bore of about the samediameter as the larger end of the conical bore in said receiving head,saidring being positioned on said receiving head so the bore in saidring is coaxial with the-conical bore in said receiving head and forms acontinuation thereof at the larger end of said conical bore.

7. A safety device according to claim 6 in which said ring is formedwith a radial portion disposed between said receiving head and saidframe and serving as a slinger ring.

I I l i

1. A safety device for a grinding machine having a frame and a spindleshaft therein and bearing means in the frame supporting the shaft withone end of the shaft projecting from the frame for receiving a grindingwheel, a receiving head seated on said projecting end of the shaft andhaving a grinding wheel mounted thereon, a threaded clamp elementthreadedly engaging the end of the shaft and clamping said receivinghead thereon and having threads of a hand such that working loads onsaid grinding wheel while it is being driven by said shaft tend totighten the threaded element on the shaft, first guiding surface meanson said receiving head coaxial with said shaft and facing away from saidframe, and second guiding surface means rigid with said frame and alsocoaxial with said shaft, said second surface facing said first surfaceand normally being spaced therefrom but cooperating therewith to provideradial support for said receiving head upon loosening of said threadedelement on said Shaft.
 2. A safety device according to claim 1 in whichsaid first and second surfaces include conical regions which taperinwardly at the same angle in a direction away from said receiving headand which are at least partly coextensive in the axial direction.
 3. Asafety device according to claim 2 in which said first and secondsurfaces also include coaxial cylindrical regions which are also atleast partly coextensive in the axial direction.
 4. A safety deviceaccording to claim 1 which includes a hood mounted on said frame and atleast partially enclosing said grinding wheel, said hood including awall portion facing that side of said grinding wheel which faces awayfrom said frame, a centering member mounted in said wall portion so asto be intersected by the extension of the axis of said shaft, and saidsecond surface being formed on said centering member.
 5. A safety deviceaccording to claim 1 in which the projecting end of said shaft has aconical seat, said receiving head having a conical bore engaging saidconical seat, and a protective element of a material softer than that ofsaid shaft fixed to said receiving head on the side thereof facing saidframe to engage said seat when said threaded element loosens to preventsaid receiving head from damaging said seat.
 6. A safety deviceaccording to claim 5 in which said protective element is in the form ofa ring and has a central bore of about the same diameter as the largerend of the conical bore in said receiving head, said ring beingpositioned on said receiving head so the bore in said ring is coaxialwith the conical bore in said receiving head and forms a continuationthereof at the larger end of said conical bore.
 7. A safety deviceaccording to claim 6 in which said ring is formed with a radial portiondisposed between said receiving head and said frame and serving as aslinger ring.